1. Field of Invention
The present invention relates to a light-transmitting color film exhibiting absorption characteristics within the visible spectrum, a method for producing the film, and a coating solution for forming the color film. More particularly, the present invention relates to a light-transmitting color film having reflectance and reflecting tone which are useful for automobile glass, a method for producing the film, and a coating solution for forming the color film.
2. Description of the Related Art
A transition metal oxide is an inorganic material exhibiting characteristic absorption within the visible spectrum. The theory explaining the absorption mechanism is as follows. When oxygen is coordinated with a transition metal, the d orbital of the transition metal is split into several energy levels. Upon splitting, coloring characteristic to the visible spectrum occurs because the electron transition energy within the orbital, which is 1-3 eV, overlaps the light energy within the visible spectrum. The same theory is considered to account for the phenomenon wherein a complex oxide including two or more kinds of transition metals absorbs visible light.
Examples of industrial application of color films using the same theory include glass products designed to have a privacy-protecting function when used for window glass of vehicles and houses, in which transmittance of visible light is reduced by means of coating transparent glass with the film, as well as glass products having a function of blocking heat rays and ultraviolet rays by shielding sunlight. Since these glass products are used for the windows of houses or vehicles, they require durability, including high wear and abrasion resistance, and high chemical resistance.
Methods for producing the above-described film include a vacuum deposition method and a sputtering method. These dry methods require expensive vacuum systems. Most glass for automobile windows is bend-processed in accordance with design requirements. Therefore, in industrial manufacturing, such glass are not a proper substrate to be processed by dry methods.
In the meantime, a thermal decomposition method is advantageous in that it provides film easily at low cost without need of expensive equipment. In the method, a starting material such as a metal salt is dissolved in a solvent, and the resultant solution is applied to a substrate and heated to high temperature, to thereby obtain metal oxide film. The method permits production of color film at low cost; however, practical application of the method has been successful only in the production of films having high reflectance.
Under these circumstances, a unique coating solution for producing color film and a method for producing color film are disclosed (J. Non-Crystalline Solids, 82, (1986), p 378-p390). The coating solution is produced by addition, to a metal salt solution used in the thermal deposition method, of a metal alkoxide which is vitrifiable by a sol-gel method.
The method is used for producing film having high wear and abrasion resistance and chemical resistance, such as Si oxide film, by use of the sol-gel method. The method is also used for producing an oxide by means of oxidizing a transition metal present in the above-described oxide film as a coloring component, by use of thermal decomposition method. In this method, for example, an Si alkoxide is added to and mixed with a solution in which nitrate salts or sulfate salts of any of several types of transition metals are dissolved as coloring components in accordance with the purpose. When a substrate is coated with the mixture of the metal salt solution and alkoxide hydrolyzate and then heated, a porous gel having a molecular structure of Sixe2x80x94Oxe2x80x94Si is produced. When the gel-coated substrate is further heated, ions of the above-described transition metal present in the porous film of the gel undergo crystallization due to heat, to thereby precipitate to form an oxide, which functions as a coloring component. In the process, the above-mentioned gel forms a hard silica film by being densificated through burning. As a result, there can be obtained a silica glass film colored with the above-described transition metal oxide and exhibiting high wear and abrasion resistance and high chemical resistance.
Production of glass by use of the sol-gel method will next be described. First, a metal alkoxide is hydrolyzed, and the hydrolyzate is polymerized, to thereby obtain a three-dimensional network including metal atoms and oxygen atoms. By allowing the reaction to proceed further, the polymer forms a gel, and the resultant porous gel is heated, to thereby produce glass or an oxide polycrystal.
One characteristic feature of the sol-gel method resides in that the method permits low-temperature synthesis. Particularly, in practice, the low-temperature synthesis of silica glass by use of Si alkoxide is widely used for forming a hard coating film on the surface of plastics.
Color films produced by use of the sol-gel method have already been proposed.
For example, Japanese Patent Application Laid-Open (kokai) No. 9406/1993 discloses a colored-glass-gel thin film comprising a metal alkoxide, a condensation polymer of the metal alkoxide, coloring matter, an alcoholic solvent, and a dispersing agent having compatibility therewith. The coloring matter has a particle size of 300-20,000 nm, and metal oxides which serve as inorganic pigments are described as materials therefor.
However, when the technique disclosed in the above-mentioned patent application is used, the particle size of the coloring matter should be adjusted so as to maintain the transparency of the colored-glass-gel thin film.
Japanese Patent Application Laid-Open (kokai) No. 208274/1996 discloses glass having an inorganic pigment including at least CuOxe2x80x94Fe2O3xe2x80x94Mn2O3 and a thin film prepared from silica sol. However, the fine-particle pigment disclosed therein (elements contained in the pigment: Cu, Mn, Co, Cr, Fe, V, Ti, and Ni) involves the following problems (1) and (2). (1) haze occurs because of scattering due to the size effect of fine particles, which is related to the refractive index of the film. (2) reduction in size of fine particles is essentially required. As a result, the absorption effect of the glass becomes low.
A method for directly forming a color film by use of a transition metal alkoxide is theoretically possible. However, although common alkoxides of Si, Ti, Al, and Zr are inexpensive and relatively easy to handle, most transition metal alkoxides are expensive and difficult to handle. Therefore, the method for producing color film directly from transition metal alkoxides cannot be used as a general method which is widely applicable.
Japanese Patent Application Laid-Open (kokai) No. 169546/1997 discloses the following technique. The specification first points out problems in the above-described techniques; xe2x80x9cWhen a silicon alkoxide and other components other than a coloring component are added in sufficient amounts such that the film attains sufficient durability, the absorbance of the film decreases. Therefore, an increase in the film thickness is required so as to obtain a required decrease in transmittance.xe2x80x9d
Claim 1 of the above publication discloses a coating solution for producing oxide film comprising one or more salts of metals selected from the group consisting of Co, Cr, Mn, Fe, Ni, Cu, Zn, and lanthanoids, and an ethylene glycol oligomer.
Further, claim 3 of the publication discloses incorporation of one or more alkoxides or chelates of metals selected from the group consisting of Si, Ti, and Zr to the coating solution.
Further, Examples 14, 15, and 16 of the publication disclose a coating solution comprising Co, Mn, and SiOR, a coating solution comprising Co, Fe, and ZrOR, and a coating solution comprising Co, Ni, and TiOR, respectively.
All films obtained from these Examples are half-mirror, brown transparent films, and have a reflectance of 20%-35%. The obtained films are described to have excellently low haze, excellent adhesion, and excellent chemical resistance.
Further, Examples 21, 22, and 23 of the publication disclose a coating solution comprising Cu, Mn, and SiOR, a coating solution comprising Cu, Mn, Co, and SiOR, and a coating solution comprising Cu, Mn, Co, Cr, and SiOR, respectively.
All films obtained from these Examples transmit light and are black in color, and have a reflectance of 8%. The obtained films are described to have excellently low haze, excellent adhesion, and excellent chemical resistance.
Further, Japanese Patent Application Laid-Open (kokai) No. 169546/1997 suggests that xe2x80x9cseveral types of metal salts may be incorporated so as to obtain a complex oxide after firing the salts.xe2x80x9d
In the method described in the above-mentioned xe2x80x9cJ. Non-Crystalline Solids,xe2x80x9d the amount of metal alkoxide to be added is required to be increased so as to improve wear and abrasion resistance and chemical resistance of the color film. However, when the amount of metal alkoxide to be added is increased in the absence of other measures, transparency of the thin film increases since the coloring of the thin film attributed to a metal oxide decreases drastically. Therefore, in order to obtain the target absorption of light, an increase in the film thickness is required. Further, the thin film produced thereby suffers a problem in that the original color of the coloring component is not reproduced in the film because the tone of color is yellowish.
In the technique disclosed in Japanese Patent Application Laid-Open (kokai) No. 169546/1997 referred to above, in Examples 14-16, and Examples 21, 22, and 24, alkoxide(s) of one or more metals selected from the group consisting of Si, Ti, and Zr are similarly incorporated into a coating solution for producing oxide film including a metal salt and ethylene glycol oligomer.
Nevertheless, in Examples 14-16 half-mirror, brown transparent films are obtained, and in Examples 21, 22, and 24 black transparent films are obtained.
The reason why the films differ in appearance and the detailed conditions for producing the respective films are not at all described in Japanese Patent Application Laid-Open (kokai) No. 169546/1997.
The inventors of the present invention have found that the film including oxides of Si, Cu, and Mn described in Example 21 generally has poor acid resistance. Addition of Co is known to be an effective measure for improving the acid resistance of the film including oxides of Cu and Mn. Thus, Example 22 of Japanese Patent application Laid-Open (kokai) No. 169546/1997 discloses film including oxides of Si, Cu, Mn, and Co.
However, when Co is added in an amount such that satisfactory acid resistance is obtained, the color tone of the film is limited to a range of gray to yellow.
Further, the inventors of the present invention have found that when the film including oxides of Si, Cu, and Mn described in Example 21 is dipped in a solution containing an electrolyte which has less ionization tendency, the metals in the film are ionized and eluted into the electrolyte. The film including oxides of Si, Cu, Mn, and Co has improved properties with respect to elution; however, the inventors found that the improvement is insufficient.
The present invention was made in an attempt to solve coating solution for forming the color film according to the present invention are characterized by incorporation of at least one organic compound having a functional group which can coordinate transition metals serving as coloring components. Further, each of the aforementioned one or more organic compounds is incorporated in an amount of 10% or more by mole with respect to the entirety of the above-described metal salts.
In order to solve the above-described problems, the present inventors have developed a light-transmitting color film which is coated on a substrate, which comprises an oxide of a network-forming element of glass (hereinafter may be simply referred to as a network-forming element or a network former) and oxides of transition metal elements serving as coloring components,
wherein the network-forming element comprises at least one element selected from the group consisting of Si, Al, and B; the total amount by mole of the network-forming element is 20-70 mol % with respect to the entirety of the elements, other than oxygen, which constitute the color film; and the amounts by mole of the transition metal elements are as described below with respect to the entirety of the elements, other than oxygen, which constitute the color film:
Cu: 10-50 mol %,
Mn: 10-50 mol %,
Ni: 1-20 mol %, and
Co: 0-20 mol %;
and the elements Cu, Mn, Ni, and Co form a complex oxide.
According to the present invention, the light-transmitting color film is produced by coating a substrate with a coating solution and firing the substrate. The coating solution comprises at least one alkoxide of Si, Al, or B as a network-forming element; transition metal salts of at least Cu, Mn, and Ni as coloring components; and at least one organic compound having a group which can coordinate the above-described transition metals.
Further, the coating solution according to the present invention comprises at least one alkoxide of Si, Al, or B as a network-forming element; transition metal salts of at least Cu, Mn, and Ni as coloring components; and at least one organic compound having a group which can coordinate the above-described transition metals.
A unique feature of the present invention resides in incorporation, as a coloring component, of Ni, and Co if desired, into a color film formed by use of a coating solution comprising as coloring components transition metal salts of primarily Cu and Mn, and a metal alkoxide.
Incorporation of Ni as a coloring component has the following effects:
(1) improvement of acid resistance
(2) attainment of the color tones of bluexe2x80x94grayxe2x80x94bronze within the range in which excellent durability is maintained.
Further, the method for forming the color film and the coating solution for forming the color film according to the present invention are characterized by incorporation of at least one organic compound having a functional group which can coordinate transition metals serving as coloring components. Further, each of the aforementioned one or more organic compounds by is incorporated in an amount of 10% or more by mole with respect to the entirety of the above-described metal salts.
The respective components forming the color film of the present invention will next be described.
Hereinafter, proportions of the elements forming the color film are represented by mol % with respect to the entirety of elements forming the film other than oxygen.
Use of Si, Al, and B is advantageous in that an oxide film containing one or more of these elements is easily produced by use of a sol-gel method. These elements serve as network formers of the color film, and presence of at least one of these elements in the color film suffices. As the total amount of the network-forming elements Si, Al, and B decreases, the reflectance of the color film increases, and the strength of the film decreases. By contrast, as the above-described total amount increases, although the strength of the film increases, the proportions of the coloring components decrease correspondingly. As a result, color film of a target transmittance cannot be produced. Further, the color film tends to add a yellowish tone.
Therefore, the range of the above-described total amount is preferably 20-70 mol %. Also, Si among the network-forming elements is preferably used.
In the present invention, at least Cu, Mn, and Ni must be incorporated as transition metal elements serving as the coloring components. Among these elements, Cu and Mn are essential components for producing a blackish color film. When the amount of Cu or Mn is less than 10 mol %, the transmittance of the color film becomes excessively high, to thereby fail to obtain a color film having a target transmittance. In contrast, when the amount of Cu or Mn is more than 50 mol %, the refractive index of the color film becomes excessively high, as does the reflectance.
Ni is required for improving chemical resistance, in particular acid resistance, of the color film. When Ni content is less than 1 mol %, the obtained colored film has a lowered resistance to a solution containing an electrolyte which has less ionization tendency. Incorporation of 4 mol % or more of Ni is preferable, in view of further improving the acid resistance of the film.
On the contrary, when the Ni content is excessively high, the film tends to exhibit excessive light transmittance and to add a yellowish tone. Therefore, the Ni content is preferably 20 mol % or less, more preferably 12 mol % or less.
Co is not an essential element. However, Co is used for adjusting the tone of the color film. When the Co content is excessively high, the total content of Cu, Mn, and Ni is correspondingly too low. Therefore, the upper limit of the Co content is 20 mol %, since the target optical characteristics are difficult to attain when the Co content is excessively high.
Organic compounds will next be described. In the present invention, the organic compound has a functional group which can coordinate the transition metals. Preferably, organic compounds having the following group: 
are used.
Particularly, the organic compound is at least one compound selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, xcex5-caprolactam, N-methylformamide, N-methylacetamide, formamide, acetamide, and 2-methylpyrrolidone.
The organic compound serves as a color coupler auxiliary agent by having a functional group which can coordinate the transition metals serving as coloring components. Addition of such an organic compound to a coating solution for forming a color film is considered to produce a color film in the following steps.
When a substrate is coated with a coating solution including, for example, an Si alkoxide, and the substrate is subsequently fired, the Si alkoxide in the solution first decomposes. The decomposed Si alkoxide thereby produces a porous gel having a molecular structure of Sixe2x80x94Oxe2x80x94Si, and is further oxidized, to thereby initiate formation of a network structure of glass. In this step, the transition metals present as coloring components in the above-described solution are not yet oxidized, because the metals are coordinated with the above-stated organic compound. When the firing proceeds further, the transition metal ions present in the porous gel crystallize while forming a complex oxide due to heat, to thereby precipitate as fine particles in the film. The precipitate serves as a coloring component. In this step, the above-mentioned gel forms a hard silica film as a result of being hardened by firing, providing a silica glass film colored by the above-described transition metal oxides and having excellent wear and abrasion resistance and chemical resistance.
Several organic compounds among those described above serve not only as color coupler auxiliary agent but also as solvents. Organic compounds in which alkoxides or transition metal salts are highly soluble and which exhibit excellent wettability to the substrate can also be used as solvents. When, for example, N-methylpyrrolidone is used, addition of a solvent is not particularly required.
Preferably, the amount of the organic compound is 10 mol % or more with respect to the total amount in mole of transition metals serving as coloring components ([total moles of an organic compound serving as a color coupler auxiliary agent/total moles of coloring components]xc3x97100 (%)). When a solvent is further added to the coating solution, incorporation of the above-described organic compound in an amount up to about 1000% is preferable. As mentioned above, when the organic compound also serves as a solvent, the upper limit thereof is not particularly limited. However, when the amount of the organic compound is excessively high, the concentrations of the coloring components become to low. Therefore, in practice, incorporation of the organic compound in an amount up to about 3000% is preferable.
The solvent will next be described.
The type of solvent to be used is not particularly limited so long as the solvent has excellent wettability to the substrate and alkoxides or transition metal salts have excellent solubility therein.
Particularly, examples of the solvent include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, cyclohexanol, methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, cellosolve acetate, diacetone alcohol, and 2-butanone.
Further, when N-methylpyrrolidone is used, ethylene glycol, hexylene glycol, and diethylene glycol monoethyl ether can also be used.
The method for coating the coating solution according to the present invention is not particularly limited. Any method can be used so long as the method is used for producing a smooth, thin, and uniform coating. Examples include spin-coating, flexo-coating, dip-coating, screen-printing, and gravure-coating.